请用ping程序的设计与实现

以下是一个简单的 Ping 程序的设计与实现，使用 Python 语言实现：

1. 导入所需的模块和库：

import os
import sys
import socket
import struct
import select
import time

2. 定义 Ping 类，包含以下方法：

- `__init__(self, destination, timeout=1, count=5, packet_size=56)`：初始化方法，用于设置 Ping 目标地址、等待超时时间、发送 Ping 包的数量和大小。

- `checksum(self, data)`：计算 ICMP 报文的校验和。

- `pack_icmp(self, id, sequence, data='')`：打包 ICMP 报文。

- `unpack_icmp(self, packet)`：解析 ICMP 报文。

- `ping(self)`：发送 Ping 包并接收响应。

- `run(self)`：启动 Ping 程序。

- `print_statistics(self)`：打印 Ping 统计信息。

class Ping:
    def __init__(self, destination, timeout=1, count=5, packet_size=56):
        self.destination = destination
        self.timeout = timeout
        self.count = count
        self.packet_size = packet_size
        self.sequence = 0
        self.id = os.getpid() & 0xFFFF

    def checksum(self, data):
        sum = 0
        for i in range(0, len(data), 2):
            sum += (data[i] << 8) + data[i+1]
        sum = (sum >> 16) + (sum & 0xFFFF)
        sum += (sum >> 16)
        return (~sum) & 0xFFFF

    def pack_icmp(self, id, sequence, data=''):
        header = struct.pack('bbHHh', 8, 0, 0, id, sequence)
        body = struct.pack('d', time.time()) + bytes(data.encode())
        checksum = self.checksum(header + body)
        header = struct.pack('bbHHh', 8, 0, checksum, id, sequence)
        return header + body

    def unpack_icmp(self, packet):
        type, code, checksum, id, sequence = struct.unpack('bbHHh', packet[:8])
        data = packet[28:]
        return type, code, checksum, id, sequence, data.decode()

    def ping(self):
        icmp_socket = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.getprotobyname('icmp'))
        icmp_socket.settimeout(self.timeout)
        for i in range(self.count):
            self.sequence += 1
            icmp_packet = self.pack_icmp(self.id, self.sequence)
            try:
                icmp_socket.sendto(icmp_packet, (self.destination, 0))
                start_time = time.time()
                ready = select.select([icmp_socket], [], [], self.timeout)
                if ready[0]:
                    packet, address = icmp_socket.recvfrom(1024)
                    elapsed_time = time.time() - start_time
                    type, code, checksum, id, sequence, data = self.unpack_icmp(packet)
                    if type == 0 and code == 0 and id == self.id and sequence == self.sequence:
                        print(f'{self.packet_size} bytes from {self.destination}: icmp_seq={sequence} time={elapsed_time:.2f} ms')
                else:
                    print(f'request timed out')
            except socket.error as e:
                print(f'{e}')
        icmp_socket.close()

    def run(self):
        print(f'PING {self.destination} ({socket.gethostbyname(self.destination)}) {self.packet_size}({self.packet_size+28}) bytes of data.')
        self.ping()
        self.print_statistics()

    def print_statistics(self):
        pass

3. 在主程序中创建 Ping 实例，并调用 `run()` 方法启动 Ping 程序：

if __name__ == '__main__':
    if len(sys.argv) != 2:
        print(f'Usage: ping.py <destination>')
        sys.exit(1)
    ping = Ping(sys.argv[1])
    ping.run()

这个 Ping 程序可以通过命令行参数指定 Ping 目标地址，例如：

python ping.py www.baidu.com